1. Field of the Invention
The present invention relates to an apparatus for heat-treating a substrate and a method for separating the substrate from the apparatus, the substrate comprising semiconductor wafers, glass substrates for LCDs, and the like.
2. Description of the Related Art
In a process for fabricating semiconductors, it is in widespread use to mount a workpiece such as semiconductor wafers, glass substrates for LCD, and the like on a workpiece-carrying platform and process the workpiece in a predetermined manner. For example, as for an apparatus for heating the substrate, several examples of such apparatus are shown in Japanese Patent Laid-Open Application Nos. Hei7-201718 and Hei6-97269, wherein an apparatus for heat-treating the substrate, i.e., a so-called hotplate is used.
FIGS. 7, 8 and 9 show an example of a conventional apparatus for heat-treating the substrate. This conventional apparatus is provided with: a workpiece-carrying platform 60 for carrying a substrate "G" as a workpiece thereon; a heater element 62 for supplying heat to the substrate "G" through the workpiece-carrying platform 60; a plurality of lift pins 70 for lifting off the substrate "G"; and, a cover member 66 for defining a processing space 64 disposed over the substrate "G" to function to expel gases produced during heating processes of the workpiece. A plurality of through-holes 68 are formed in both the workpiece-carrying platform 60 and the heater element 62. In each of these through-holes 68, each of the lift pins 70 is inserted so as to be capable of moving up and down relative to the through-hole 68. In operation, when the lift pin 70 is moved up and down by a piston 78 of a cylinder mechanism 76, the substrate "G" is transferred from the workpiece-carrying platform 60 to an outside means or vice versa.
In this case, the workpiece-carrying platform 60 is constructed of a square-shaped aluminum alloy plate which is excellent in thermal conductivity and surfaced with an aluminum oxide coating. Further, as shown in FIG. 8, a surface of the workpiece-carrying platform 60 is roughed by the provision of a plurality of concentric annular grooves 71. On the other hand, the heater element 62 is also constructed of an aluminum alloy plate which assumes substantially the same shape in plan view as that of the workpiece-carrying platform 60. Incorporated in this heater element 62 is a heater.
Further, as shown in FIG. 7, a sleeve-like shutter member 80 is disposed around an outer peripheral portion of the workpiece-carrying platform 60 so as to be capable of moving up and down relative to the workpiece-carrying platform 60. This shutter member 80 is connected with a piston 82 of a shutter drive cylinder 82 capable of moving the shutter member 80 up and down. Consequently, it is possible to control the volume of the processing space 64 by moving the shutter member 80 up and down.
Further, as shown in FIG. 8, also provided in an upper surface of the workpiece-carrying platform 60 is a spacer 85 for preventing the substrate "G" from being brought into contact with the workpiece-carrying platform 60. The spacer 85 extends along an outer peripheral portion of a workpiece (i.e., substrate "G") carrying area of the workpiece-carrying platform 60. This spacer 85 is constructed of a flat oval-shaped ceramic segment, and provided with a plurality of through-holes in its end portions, in each of which through-holes a mounting screw 86 is inserted and threadably engaged with a threaded hole 87 formed in the upper surface of the workpiece-carrying platform 60.
Now, the apparatus for heat-treating the substrate "G" will be described in operation.
First, the substrate "G" mounted on the workpiec-carrying platform 60 is transferred to the lift pins 70 having been moved up. When the lift pins 70 are moved down, the substrate "G" is mounted on the spacer 85 over the workpiece-carrying platform 60. Then, the shutter is driven so that a processing section of the apparatus is partitioned off from the outside. In this processing section of the apparatus, heat from the heater element 62 is transmitted to the workpiece-carrying platform 60, and further to the substrate "G" through the upper surface of the workpiece-carrying platform 60. In this case, since heat transmission from the heater element 62 to the workpiece-carrying platform 60 is accomplished through the entire contact surfaces comprising the lower surface of the workpiece-carrying platform 60 and the upper surface of the heater element 62, the workpiece-carrying platform 60 is uniformly heated as a whole. Consequently, the distribution of heat transmitted from the heater element 62 to the substrate "G" through the workpiece-carrying platform 60 is uniform, so that the substrate "G" is uniformly heat-treated.
After completion of the above heat treatment, the substrate "G" is separated from the workpiece-carrying platform 60 when the lift pins 70 are lifted. At this time, however, since the substrate "G", which tends to bear electrostatic charges, is attracted to the surface of the workpiece-carrying platform 60 due to electrostatic charges. Due to such attraction, it is hard to separate the substrate "G" from the workpiece-carrying platform 60, which often causes misalignment in location of the substrate "G", and/or damage of a device due to drop of the substrate "G". Further, there are fears that due to built-up electrostatic charges, fine dirt is attracted, and that due to electrostatic discharge, the device is destroyed.
In this respect, in the above conventional apparatus, since the grooves 71 are provided to such an extent as not to disturb the uniformity in temperature of the surface of the workpiece-carrying platform 60, the build-up of electrostatic charges is suppressed to some extent. Due to this, it is possible to suppress in occurrence the above-mentioned problems.
However, such a provision of the grooves 71 only in the surface of the workpiece-carrying platform 60 is not sufficient to suppress the build-up of the electrostatic charges.
Consequently, the above-mentioned problems inherent in the conventional apparatus are still not completely solved.